1. Field of the Invention
This invention relates to vibrating conveyors and, in particular, to an improved drive mechanism suitable for use in circular and helical vibrating conveyors.
2. Discussion of the Prior Art
In contrast to movement along straight line vibrating conveyors, articles on a circular conveyor must be given a vibrating motion which causes the articles to move continuously in a circle. Thus, the motion must be both vertical and twisting in the horizontal plane. Various types of vibrating drives used with circular conveyors, particularly spiral type vibrating conveyors, may be found in the patent literature, such as in U.S. Patent Office classification 198, subclass 756. It is known, for example, to provide the desired motion with a pair of generally parallel, contra rotating shafts mounted on a helical conveyor transversely to its vertical axis with each of the shafts carrying a pair of eccentric weights. The weights are phased so that the horizontal resultant of the forces on each side of the conveyor are generally parallel to the helix. This produces the circular motion. Similarly, the vertical components are in phase. Collectively, the vertical component is upward when the horizontal component is in the direction of the helical ascendency and downward with the horizontal component is in the direction of helical descendency.
A typical helical drive of the above type is described in U.S. Pat. No. 2,927,683. A motor is connected to and drives each shaft. As the patentee states, a problem with this type of drive is that a precessional force is created and acts on the eccentric weights. The force results not only in possible shaft breakage but considerable increased load against the shaft bearings. For large helical conveyor assemblies, the load increase may become significant and affect the performance of the assembly.
It is therefore a paramount object of the present invention to provide for a drive of the type described above which reduces or eliminates thrust bearing loads in helical conveyor assemblies.